FIG. 1 depicts a left side cutaway view of a conventional gas turbine engine 100 including a conventional accessory gearbox (AGB) 40 mounted thereon. The conventional gas turbine engine 100 comprises an air inlet 25, a compressor section 5, a combustion section 10, and a turbine section 15, arranged sequentially in that order. All of these sections are generally cylindrical and oriented coaxially. The conventional gas turbine engine further comprises an exhaust plenum 20, and the AGB 40. The compressor 5, the turbine 15 and the AGB 40 are all coaxially coupled by the main engine shaft 30 (shown only in part in the interest of brevity and clarity). With the exception of the AGB 40, the entire engine is enclosed in an engine casing 50.
The accessory gearbox (AGB) 40 drives various accessory devices 42 essential for the engine and for aircraft operation. Such accessory devices 42 include, for example, tachometers, generators (alternators), hydraulic pumps, fuel pumps, oil pumps, fuel controls, starters, Permanent Magnet Generators (PMA), and (in some instances) water pumps, etc. Accessory devices may operate at different rotational speeds and powers. The accessory devices, the AGB 40 and the engine casing 50 (inclusive of the engine) must all fit with the confines of an aerodynamic nacelle or within an engine bay. A nacelle is a cover housing that is separate from the aircraft fuselage that holds engines, fuel, or equipment.
A towershaft 35 driven by a first set of bevel gears 36 off of the main engine shaft 30 is typically used to transfer power from the main engine shaft 30 to the AGB 40. The conventional AGB has at least one gear axis 41 running in a plane parallel with the main engine shaft 30. More specifically, the towershaft transfers power from the main engine shaft 30 to a second set of bevel gears 38 mounted inside the AGB 40. Driven by the second set of bevel gears, generally parallel with the main engine axis 30 and either perpendicular or canted in relation to the towershaft, is an input drive shaft 43. Integral to this shaft is an accessory input spur gear that drives a spur gear train (see FIG. 1A) that supplies power to the plurality of accessory devices 42 installed on the AGB 40. Accessory devices may be mounted to the forward and aft faces of the conventional AGB (e.g., a pair of accessory devices 42 are depicted in FIG. 1, one of the accessory devices 42 depicted on the AGB forward face and the other accessory device of the pair of accessory devices depicted on the AGB aft face).
Each of the accessory devices 42 driven by the conventional AGB 40 are arranged in a direction parallel with the main shaft 30 and are dispersed arcuately around the engine casing 50 and locally radially away from the main engine shaft 30. This arrangement permits the accessory devices 42 to fit between a wall of an engine bay and the engine casing 50, but requires a large amount of space within the engine nacelle. In addition, the number of accessory devices, their rotational speed, and power required to turn, combined with the conventional AGB arrangement (whereby the second set of bevel gears are used in right angle configurations, and the towershaft and input drive shaft are arranged either perpendicular or at a canted angle to each other generally replicating the angle of the towershaft to the main engine shaft 30), can increase the size and weight of the AGB. With conventional AGBs, there are also concerns about the ease of access to the accessory devices and their installation/removal, and the layout of associated hoses and electrical connectors and accessory cooling, making the packaging of the accessory devices, the AGB, and the gas turbine engine within the engine nacelle a complicated task.
Accordingly, it is desirable to provide improved accessory gearboxes of mechanical drive systems and gas turbine engines including the same.